Amorphous alloy powder core and nano-crystal alloy powder core having good high frequency properties and methods of manufacturing the same

ABSTRACT

A method of manufacturing an amorphous alloy core including the steps of mixing an amorphous alloy powder with a solution made by dissolving a polyimide/phenolic resin binder in an organic solvent, evenly coating the binder in liquid phase on the surface of the alloy powder to make a powder of composite particles, molding the power of composite particles, and performing a heating treatment thereon. This invention also discloses a method of manufacturing a nano-crystal alloy core including the steps of (a) mixing an amorphous alloy powder with a solution made by dissolving a polyimide/phenolic resin binder in an organic solvent, evenly coating the binder in the liquid phase on the surface of the alloy powder to make composite particles, molding the composite particles at room temperature, and performing a heating treatment thereon at a temperature higher than the crystallization starting temperature of the alloy; and (b) performing a heating treatment on an amorphous alloy powder at over a crystallization starting temperature to make a nano-crystal phase, mixing a solution made by solving a polyimide/phenolic resin binder in an organic solvent therewith, evenly coating the binder in liquid phase on the surface of the alloy powder to make composite particles, and molding the power of composite particles at 100 to 300° C.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to an amorphous alloy powder corehaving excellent high frequency properties and a nano-crystal alloypowder core with excellent soft-magnetic properties in the highfrequency band range, and also relates to methods of manufacturing thesame. More specifically, the present invention relates to a method ofmanufacturing an amorphous alloy powder core with good high frequencyproperties that can be made by low-temperature compression molding, byusing a small amount of a polyimide resin or a phenolic resin binderwith a crystalline magnetic core material, with the further benefit thatthe production yield is enhanced. The present invention also relates toa method of manufacturing a nano-crystal alloy powder core withexcellent saturated magnetic flux density and effective permeability byperforming a heat treatment of an amorphous alloy powder or an amorphousalloy powder core at a temperature greater than the crystallizationtemperature of the alloy.

[0003] (b) Description of the Related Art

[0004] Generally, amorphous soft-magnetic alloys exhibit excellentcorrosion resistance and abrasion resistance, as well as strength andpermeability, and are used as magnetic materials for electric andelectronic appliances. They can be applied to transformers, inductors,motors, generators, relays, etc. Such amorphous soft-magnetic alloys arequenched during manufacture in order to maintain the amorphous state,and are generally formed in the shape of thin bands or fine lines. Tomanufacture a core of a particular shape, the amorphous soft-magneticalloy used to form the shape is first ground to powder and is thencompressed under a given pressure at a given temperature.

[0005] The bulk molding of the amorphous soft-magnetic alloy powdershould be carried out at a temperature lower than the crystallizationpoint for the alloy so as to maintain its amorphous state. However,since it is impossible to bulk mold the alloy powder at such atemperature, a method of binding the amorphous soft-magnetic alloypowder has been employed, in which a glass powder with a lowervitrification point than that of the amorphous soft-magnetic alloypowder was added by means of a ball mill, after which the resultingpowder was softened and pressed at a temperature of about 500° C. Hotisostatic pressing (HIP), and a hot press, etc. are generally used forthe above method. There are other methods such as an explosive method,and an impact gun method, however special equipment is necessary toattain very high energy and the practice of these methods is timeconsuming, thus lowering the production yield.

[0006] Bulk molding of crystalline soft-magnetic alloy powder is carriedout at a high temperature and uses, eg. a water glass as a binder. Thisis because the alloy powders are amenable to plastic deformation andstrongly hold together during pressing at pressures of over 15 ton/cm²,since the crystalline alloy is lower in strength than the amorphousalloy. This process causes fewer cracks and the heating treatment aftermolding can be conducted at a high temperature of about 800° C. to bringabout the diffusion of atoms and to thereby attain stronger bondsbetween particles.

[0007] On the other hand, if one were to perform high-pressure moldingof an amorphous alloy powder that has very high strength and ductilitycompared to the crystalline material, and were to use water glass as abinder, numerous cracks would be produced in the core. In addition,since the heating treatment that is carried out at below 500° C. doesnot bring about diffusion of atoms, the final core would be very low instrength and easily broken.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide a method ofmanufacturing an amorphous alloy powder core with good high frequencyproperties that can be made through low-temperature compression moldingby using a polyimide resin or a phenolic resin with higher viscositythan a conventional water glass as a binder, thereby reducing the amountof the required binder, and assuring a higher production yield than isachieved with hot isostatic pressing.

[0009] It is another object of the present invention to provide anamorphous alloy core having a high molding density and no surfacecracks, and that exhibits a low dependence on frequencies and constantpermeability even in the high frequency band range because of theimproved insulative properties of the alloy core particles.

[0010] It is still another object of the present invention to provide amethod of manufacturing a nano-crystal alloy powder core with excellentsaturated magnetic flux density and enhanced effective permeability byheat treating an amorphous alloy powder at a temperature higher than thecrystallization starting temperature of the alloy and by using apolyimide resin or a phenolic resin as a binder.

[0011] It is still another object of the present invention to provide anano-crystal alloy powder core having a high molding density and nosurface cracks, and showing a low dependence on frequencies and constantpermeability even in the high frequency band range because of theimproved insulative properties of the alloy core particles.

[0012] In order to achieve the above objects, the present inventionprovides a method of manufacturing an amorphous alloy core including thesteps of mixing an amorphous alloy powder with a solution made bydissolving a polyimide/phenolic resin binder in an organic solvent,evenly coating the surface of the alloy powder with the binder in liquidphase to make composite particles, molding the composite particles, andperforming a heat treatment thereon.

[0013] Preferably, the above method may further include the steps ofheat treating the amorphous alloy powder at a temperature of less than500° C. before mixing the amorphous alloy powder in the solution made bydissolving the polyimide resin or phenolic resin in the organic solvent.

[0014] Molding may be performed at a temperature of less than 200° C.and under a pressure of 10 to 50 ton/cm². The heat treatment isperformed at 150 to 500° C.

[0015] The amorphous alloy core has a saturated magnetic flux density ofmore than 0.80T and a permeability of more than 0.90, measured in 1 MHzand 0.1 MHz.

[0016] According to another aspect of the present invention, a method ofmanufacturing a nano-crystal alloy core includes the steps of mixing anamorphous alloy powder with a solution made by solving apolyimide/phenolic resin binder in an organic solvent, evenly coatingthe surface of the alloy powder with the binder in liquid phase to formcomposite particles, molding the composite particles at a normaltemperature. and performing a heating treatment thereon at a temperaturethat is higher than the crystallization starting temperature of thealloy.

[0017] According to still another aspect of the present invention, amethod of manufacturing a nano-crystal alloy core includes the steps ofheat treating an amorphous alloy powder at a temperature of over itscrystallization starting temperature to form a nano-crystal phase,mixing a solution made by dissolving a polyimide/phenolic resin binderin an organic solvent therewith, evenly coating the surface of the alloypowder with the binder in liquid phase to make composite particles, andmolding the composite particles at 100 to 300° C. The molding isperformed under a pressure of 10 to 50 ton/cm² for less than 1 minute.

[0018] The resulting nano-crystal alloy core has a saturated magneticflux density of more than 1.10T and a permeability of more than 0.90, asmeasured at 1 MHz and 0.1 MHz. The properties of the nano-crystal alloycore of the invention are enhanced by more than 20% compared to theamorphous alloy powder core of the same composition prepared byconventional methods.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In the following detailed description, preferred embodiments ofthe invention have been shown and described, simply by way ofillustration of the best mode contemplated by the inventor(s) ofcarrying out the invention. As will be realized, the invention iscapable of modification in various obvious respects, all withoutdeparting from the spirit or essential characteristics of the invention.

[0020] The types of alloy powders, binders, their amounts, and thepressing conditions required for the practice of the methods ofmanufacturing amorphous alloy powder cores and nano-crystal alloy powdercores of this invention are similar throughout the steps in themanufacture of each core. The amorphous alloy powder can be made by amechanical alloy process, a rapid solidification, a water injectionprocess, and the like.

[0021] Suitable alloy powders include and may be selected from Fe basedpowders (Fe—Si—B based, Fe—Al—B based, etc.), Co based powders(Co—Fe—Si—B based) that are preferable alloy powders for the preparationof products in the amorphous state, and Fe—Si—B based powders, Fe—Al—Bbased powders, and the like, that are preferable alloy powders for thepreparation of products characterized by nano-crystallization ofamorphous powders through appropriate heating treatment. Thecrystallization temperature for these alloys is about 500° C. Thepreparation of an amorphous alloy powder by high pressure waterinjection comprises grinding a dropping stream of molten metal at apressure of over 30 Mpa, and then quenching the stream. High pressurewater injection results in higher product yield and suppression ofcrystallization in distinction to conventional techniques. Using highpressure water injection, one can manufacture amorphous alloy powderswith various average diameters less than 100 μm in response to avariation of the injection conditions.

[0022] The vitrification point of the binder should be lower than thecrystallization temperature of the amorphous alloy, and the binder musthave a binding strength at a normal temperature that is sufficient torestrain generation of cracks, thereby retaining the shape of the coreunder the applied pressure at the normal temperature. It is preferablethat a polyimide-based thermosetting resin or a phenol-based or phenolicthermosetting resin is used as a binder. Suitable polyimide resinsinclude homopolymers and copolymeric formulations, with a particularnon-limiting example of such a resin comprising ULTEM 1000, manufacturedby GE Plastics. Suitable phenolic resins include phenol-formaldehyde,resorcinol-formaldehyde and the like, and by way of non-limitingillustration, a particular phenolic resin is KMB-100PLM manufactured byKolon Chemical.

[0023] It is preferable that the amount of the binder ranges from 0.5 to3.0 wt % of the total mass. It is hard to mold the alloy powder into acohesive body if the amount of the binder is less than 0.5 wt % becauseof a weak binding strength. On the contrary, if the amount of the binderis too large, the amount of the alloy powder forming the final productis reduced, and its soft-magnetic properties are undesirably diminishedeven though the binding strength between the alloy powder particlesbecomes high. The above-described total mass refers to the mass of allthe binder and alloy powder forming the core, and does not include themass of an organic solvent.

[0024] It is preferable that a pressure of 10 to 50 ton/cm² is requiredfor molding an alloy powder manufactured by mixing a binder therein. Ifthe pressure is less than 10 ton/cm², the density of the core becomestoo low and the soft magnetic property of the core is degraded. If thepressure is too high, the die surface is greatly abraded and its usefullife is reduced, and the production cost is thus increased.

[0025] In the manufacture of the inventive amorphous/nano-crystal alloypowder products having excellent high frequency properties,manufacturing conditions such as molding temperature, the temperaturefor the heat treatment of the core, and the like, may vary with regardto the particular amorphous or nano-crystal alloy powder core underpreparation.

[0026] First, it is preferable that the molding temperature formanufacturing the inventive amorphous alloy powder core is lower than200° C. The higher the pressing temperature is, the higher the moldingdensity of the core becomes as a function of the increased density ofthe powder particles. If the temperature is higher than 200° C., theenergy cost becomes high, which is not preferable.

[0027] The temperature for the heating treatment in the manufacture ofthe inventive amorphous alloy powder core varies with the components ofthe amorphous alloy and temperatures required for previous treatments,and is preferably 150 to 500° C., which is lower than thecrystallization temperature by 50 to 200° C. If the temperature is toolow, the internal stress produced during molding is not fully removed.If the temperature is too high, phase transformation from the amorphousstate and the formation of crystal structures may occur. The heattreatment is carried out in an ambient atmosphere of inert gas orreducing gas for a period of time or from 5 to 60 minutes. If the periodof time for the heating treatment is too short, the stress is not fullyremoved, with the result that the heat treatment would be undesirablyprolonged and the production yield would be decreased.

[0028] The following describes the manufacture of a nano-crystal alloypowder core with excellent soft-magnetic properties in the highfrequency band range. In the method of manufacturing a core by (a)performing a heating treatment on an amorphous alloy powder attemperature above the crystallization starting temperature to make anano-crystal alloy powder, mixing it with a solution made by dissolvinga polyimide/phenolic resin binder in an organic solvent, and evenlycoating the binder in liquid phase on the surface of the above alloypowder to make a powder of composite particles. The heat treatmenttemperature is preferably higher than the vitrification point of thebinder. If the temperature is high, the molding density of the core andthe density of the particles become high, and if it is higher than 300°C., the energy cost becomes high. The temperature for the heatingtreatment is higher than the crystallization starting point andparticularly, is up to but less than 100° C., and more preferably by 50°C.

[0029] Generally, the heating treatment for metal alloys is preferablyperformed at about 500 to 600° C. If the temperature for the heatingtreatment is too far above the crystallization starting temperature, thecrystal phase becomes abruptly coarse, and the binder is abruptlydissolved, thus decreasing the bond strength between the particles. Ifthe temperature is lower than the crystallization starting point, anano-crystal phase is hardly produced. Preferably, the heating treatmentis performed in an ambient atmosphere of a reducing gas for a period oftime of from 10 to 60 minutes. If the time for the heating treatment istoo short, the stress cannot be fully removed, with the result that theheat treatment would be undesirably prolonged and the production yieldwould be decreased.

[0030] The following describes the manufacture of a nano-crystal alloypowder core with excellent soft-magnetic properties in the highfrequency band range. In the method of manufacturing such a nano-crystalalloy powder core by (b) mixing an amorphous alloy powder with asolution made by dissolving a polyimide/phenolic resin binder in anorganic solvent, evenly coating the binder in liquid phase on thesurface of the alloy powder to make a powder of composite particles,molding the composite particles at a normal temperature, and then heattreating the amorphous alloy powder at a temperature higher than itscrystallization starting temperature i.e. the temperature at whichcrystallization begins, more particularly, the temperature required forthe heat treatment is higher than the crystallization starting point(e.g. by about 100° C.), and preferably, by 50° C. Generally, the heattreatment of the metal alloy is preferably performed at about 500 to600° C. The following non-limiting examples are presented to illustratethe practice of the present invention.

EXAMPLES OF PREPARATION OF INVENTIVE AMORPHOUS ALLOY POWDER CORESExample 1

[0031] A solution made by dissolving 1 g of a polyimide resin (ULTEM1000, GE Plastic) in a 100 cc solution of methylene chloride is combinedwith Fe₇₃Si₁₃B₁₀Nb₃Cu₁ amorphous alloy powder (average diameter about 15μm) of 99 g prepared by a high pressure water injection process, and theresulting combination is mixed for about 10 minutes. The mixture is thendried, thus yielding a powder of composite particles with polyimideevenly coated on their surface to a thickness of less than 1 μm. Theparticles have an average diameter of 15 μm.

[0032] A quantity of the composite particles (7 g) is inserted into adie with an outer diameter of 20 mm and an inner diameter of 12 mm andmolded under a pressure of 20 ton/cm² at room temperature, and thenthermally treated at 450° C. for 30 minutes in an ambient atmosphere ofAr gas, thus making an amorphous core. The properties of the amorphouscore, i.e. density, generation of cracks, saturated magnetic fluxdensity, effective permeability in various frequency bands, andpermeability ratio (μ_(1 MHz)/μ_(0 1 MHz)) are shown in Table 1. Thedensity of the core is a value obtained by dividing the actual mass ofthe core by its volume, and the saturated magnetic flux density (B_(s))is measured under an external magnetic field of 5,000 Oe by using avibrating sample magnetometer (VSM). The effective permeability ismeasured in each frequency band under an external magnetic field of 10mOe by using an LCR meter. The permeability ratio(μ_(1 MHz)/μ_(0 1 MHz)) is a ratio of permeability values measured in 1MHz and 0.1 MHz.

Example 2

[0033] This example is carried out under the same conditions as those ofExample 1 except that a solution is made by dissolving 0.5 g of thepolyimide resin in a solution of 100 cc methylene chloride. Theproperties manufactured amorphous core, i.e. density, generation ofcracks, saturated magnetic flux density, effective permeability invarious frequency bands, and permeability ratio (μ_(1 MHz)/μ_(0 1 MHz))are shown in Table 1.

Example 3

[0034] This example is carried out under the same conditions as those ofExample 1 except that a solution is made by dissolving 1.5 g of thepolyimide in a 100 cc solution of methylene chloride. The properties ofthe manufactured amorphous core, i.e. density, generation of cracks,saturated magnetic flux density, effective permeability in variousfrequency bands, and permeability ratio (μ_(1 MHz)/μ_(0 1 MHz)) areshown in Table 1.

Example 4

[0035] This example is carried out under the same conditions as those ofExample 1 except that the molding pressure at room temperature is 10ton/cm². The properties of the manufactured amorphous core, i.e.density, generation of cracks, saturated magnetic flux density,effective permeability in various frequency bands, and permeabilityratio (μ_(1 MHz)/μ_(0 1 MHz)) are shown in Table 1.

Example 5

[0036] This example is carried out under the same conditions as those ofExample 1 except that the pressure at room temperature is 40 ton/cm².The properties of the manufactured amorphous core, i.e. density,generation of cracks, saturated magnetic flux density, effectivepermeability in various frequency bands, and permeability ratio(μ_(1 MHz)/μ_(1 MHz)) are shown in Table 1.

Example 6

[0037] An amount of 99 g of Fe₇₃Si₁₃B₁₀Nb₃Cu₁ amorphous alloy powder(average diameter about 15 μm) prepared by a high pressure waterinjection process is thermally treated at 450° C. for 30 minutes in anambient atmosphere of Ar gas, and air cooling is then performed thereonat room temperature. A solution made by dissolving 1 g of a phenol resin(KMB-100PLM, KOLON Chemical) in 100 cc of methyl alcohol is mixedtherewith for 10 minutes. The mixture is then dried, thus yielding apowder of composite particles with phenol evenly coated on the surfaceof the amorphous alloy powder (average diameter 15 μm) to a thickness ofless than 1 μm.

[0038] A quantity of 7 g of composite particles is inserted into a diewith an outer diameter of 20 mm and an inner diameter of 12 mm, and ismolded under a pressure of 20 ton/cm² at room temperature, and is thenthermally treated at 150° C. for 10 minutes in an ambient atmosphere ofAr gas, thus making an amorphous core. The properties of the amorphouscore, i.e. density, generation of cracks, saturated magnetic fluxdensity, effective permeability in various frequency bands, andpermeability ratio (μ_(1 MHz)/μ_(1 MHz)) are shown in Table 1.

Example 7

[0039] This example is carried out under the same conditions as those ofExample 6 except that a solution is made by dissolving 0.5 g phenol in100 cc of methyl alcohol. The properties of the manufactured amorphouscore, i.e. density, generation of cracks, saturated magnetic fluxdensity, effective permeability in various frequency bands, andpermeability ratio (μ_(1 MHz)/μ_(0 1 MHz)) are shown in Table 1.

Example 8

[0040] This example is carried out under the same conditions as those ofExample 6 except that a solution is made by dissolving 1.5 g phenol in100 cc of methyl alcohol. The properties of the manufactured amorphouscore, i.e. density, generation of cracks, saturated magnetic fluxdensity, effective permeability in various frequency bands, andpermeability ratio (μ_(1 MHz)/μ_(0 1 MHz)) are shown in Table 1.

Example 9

[0041] This example is carried out under the same conditions as those ofExample 6 except that the temperature of the die is kept at 150° C. andthe next heating treatment is omitted. The properties of themanufactured amorphous core, i.e. density, generation of cracks,saturated magnetic flux density, effective permeability in variousfrequency bands, and permeability ratio (μ_(1 MHz)/μ_(0 1 MHz)) areshown in Table 1.

Example 10

[0042] This example is carried out under the same conditions as those ofExample 6 except that an amorphous alloy powder having the samecomposition as that of the alloy of Example 1 was used that wasthermally treated at 450° C. for 30 minutes in an ambient atmosphere ofH₂ gas, and air cooling was performed thereon at room temperature. Theproperties of the manufactured amorphous core, i.e. density, generationof cracks, saturated magnetic flux density, effective permeability invarious frequency bands, and permeability ratio (μ_(1 MHz)/μ_(1 MHz))are shown in Table 1. TABLE 1 Saturated Permeability Density GenerationMagnetic Effective Permeability (μ) Ratio Example (g/cm²) of Cracks FluxDensity 0.1 MHz 0.5 MHz 1 MHz μ_(1 MHz)/μ_(0 1 MHz) 1 5.74 No 0.90 T45.2 45.0 44.7 0.99 2 5.83 No 0.91 T 51.1 51.0 50.6 0.99 3 5.67 No 0.90T 43.0 43.0 42.8 1.00 4 4.90 No 0.80 T 35.0 35.0 34.7 1.00 5 6.16 No0.96 T 97.5 97.5 91.9 0.94 6 5.73 No 0.89 T 44.7 44.7 44.0 0.98 7 5.87No 0.91 T 56.0 56.0 54.5 0.96 8 5.68 No 0.90 T 42.2 42.2 42.0 1.00 95.93 No 0.92 T 61.7 61.7 59.2 0.95 10 5.74 No 0.85 T 47.8 47.8 47.3 1.00

[0043] Referring to Table 1, the saturated magnetic flux density in allof the illustrated examples is about 0.90T, and higher than 0.8T, anaverage of the well-known crystalline soft-magnetic alloy powder core.There is little permeability change in the frequency band from 0.1 MHzto 1 MHz. The permeability ratio of this core is over 0.90 in thefrequency band of 1 MHz and 0.1 MHz, and shows the low dependence of theinventive core on frequencies, which means that this amorphous core canbe used tol MHz. When comparing it with a conventional metal crystalcore, the inventive core is similar to or superior to the metal crystalcore in magnetic properties (saturated magnetic flux density andpermeability), and its effective permeability ratio is over 0.90 in thefrequency band to 1 MHz. Therefore, the inventive core can be used intens of megahertz whereas the metal crystal core's appropriate frequencyband is 200 kHz.

COMPARATIVE EXAMPLES OF PREPARATIONS OF AMORPHOUS ALLOY POWDER CORESComparative Example 11

[0044] This comparative is carried out under the same conditions asthose of Example 1 except that a solution is made by dissolving 0.3 g ofthe polyimide of Example 1 in a 100 cc solution of methylene chloride.The properties of the manufactured amorphous core, i.e. density,generation of cracks, saturated magnetic flux density, effectivepermeability in various frequency bands, and permeability ratio(μ_(1 MHz)/μ_(0 1 MHz)) are shown in Table 2.

Comparative Example 12

[0045] This comparative example is carried out under the same conditionsas those of Example 1 except that a solution is made by dissolving 3.2 gpolyimide in a 100 cc solution of methylene chloride. The properties ofthe manufactured amorphous core, i.e. density, generation of cracks,saturated magnetic flux density, effective permeability in variousfrequency bands, and permeability ratio (μ_(1 MHz)/μ_(0 1 MHz)) areshown in Table 2.

Comparative Example 13

[0046] This comparative example is carried out under the same conditionsas those of Example 1 except that the molding pressure at roomtemperature is 5 ton/cm². The properties of the manufactured amorphouscore, i.e. density, generation of cracks, saturated magnetic fluxdensity, effective permeability in various frequency bands, andpermeability ratio (μ_(1 MHz)/μ_(0 1 MHz)) are shown in Table 2.

Comparative Example 14

[0047] This comparative example is carried out under the same conditionsas those of Example 6 except that the solution is made by dissolving 0.3g phenol in 100 cc of methyl alcohol. The manufactured properties of theamorphous core, i.e. density, generation of cracks, saturated magneticflux density, effective permeability in various frequency bands, andpermeability ratio (μ_(1 MHz)/μ_(1 0 MHz)) are shown in Table 2.

Comparative Example 15

[0048] This comparative example is carried out under the same conditionsas those of Example 6 except that a solution is made by dissolving 3.2 gphenol in 100 cc of methyl alcohol. The properties of the manufacturedamorphous core, i.e. density, generation of cracks, saturated magneticflux density, effective permeability in various frequency bands, andpermeability ratio (μ_(1 MHz)/μ_(1 0 MHz)) are shown in Table 2. TABLE 2Saturated Permeability Comparative Density Generation of MagneticEffective Permeability (μ) Ratio Example (g/cm²) Cracks flux Density 0.1MHz 0.5 MHz 1 MHz μ_(1 MHz)/μ_(0 1 MHz) 11 4.85 Numerous 0.78 T 17.617.6 17.6 1.00 Cracks 12 4.90 NO 0.88 T 26.7 26.7 26.7 1.00 13 4.50 NO0.70 T 17.3 17.3 17.3 1.00 14 4.86 Numerous 0.78 T 16.4 16.4 16.4 1.00Cracks 15 4.87 NO 0.88 T 27.2 27.2 27.2 1.00

[0049] Referring to Table 2, numerous cracks were generated in certainof the comparative cores (see Examples 11 and 14), and the effectivepermeability and saturated magnetic flux density were abruptlydecreased.

PREPARATIONS OF INVENTIVE NANO-CRYSTAL ALLOY CORES Example 16

[0050] A solution made by dissolving 1 g of the polyimide used inExample 1 in a 100 cc solution of methylene chloride and combining suchsolution with 99 g Fe₇₃Si₁₃B₁₀Nb₃Cu₁ amorphous alloy powder (averagediameter about 15 μm) prepared by a high pressure water injectionprocess, following which the resulting combination is mixed for about 10minutes. The mixture is then dried, thus yielding composite particles ofamorphous alloy powder with polyimide evenly coated on their surface toa thickness of less than 1μm, the particles having an average diameterof 15 μm.

[0051] Next, 7 g of the powder of composite particles is inserted into adie with an outer diameter of 20 mm and an inner diameter of 12 mm andmolded under a pressure of 20 ton/cm² at a room temperature, and thenthermally treated at 560° C. for 30 minutes in an ambient atmosphere ofAr gas, to form the nano-crystal core. The properties of thenano-crystal core, i.e. density, generation of cracks, saturatedmagnetic flux density, effective permeability in various frequencybands, and permeability ratio (μ_(1 MHz)/μ_(1 0 MHz)) are shown in Table3.

[0052] The crystallization starting temperature for the amorphous powderis measured by heating at a heating speed of 2° C./min through adifferential temperature analysis (DTA). The average size of a crystalgrain is the value of the average diameter measured by X-ray diffraction(XRD) and a transmission electron microscope (TEM). The density of thecore is the value obtained by dividing the core's actual mass by thecore's volume, and the saturated magnetic flux density (B_(s)) ismeasured under an external magnetic field of 5,000 Oe by using VSM.Effective permeability is measured in each frequency band under anexternal magnetic field of 10 mOe by using an LCR meter. Thepermeability ratio (μ_(1 MHz)/μ^(0 1 MHz)) is a ratio of permeabilityvalues measured at 1 MHz and 0.1 MHz.

Example 17

[0053] This example is carried out under the same conditions as those ofExample 16 except that 99 g Fe₈₀Al₄B₁₀Zr₅Cu₁ amorphous alloy powder(average diameter about 12 μm) prepared by the high pressure waterinjection process is thermally treated at 500° C. for 30 minutes in anambient atmosphere of Ar gas.

Example 18

[0054] In this example 99 g of Fe₈₀Al₄B₁₀Zr₅Cu₁ amorphous alloy powder(average diameter about 12 μm) prepared by a high pressure waterinjection process, is thermally treated at 500° C. for 30 minutes in anambient atmosphere of Ar gas, and is then air cooled at roomtemperature. A solution made by dissolving 1 g of phenol in 100 cc ofmethyl alcohol is mixed therewith for 10 minutes. The mixture is thendried, yielding composite particles having an average diameter of 12 μm,with phenol evenly coated to a thickness of less than 1 μm. on thesurface of the amorphous alloy powder.

[0055] Seven grams of composite particles are inserted into a die withan outer diameter of 20 mm and an inner diameter of 12 mm, and moldedunder a pressure of 20 ton/cm² at 150° C., thus forming an amorphouscore.

[0056] The properties of the amorphous core, i.e. density, generation ofcracks, saturated magnetic flux density, effective permeability invarious frequency bands, and permeability ratio (μ_(1 MHz)/μ_(0 1 MHz))are shown in Table 3.

Example 19

[0057] This example is carried out under the same conditions as those ofExample 16 except that the molding pressure is 40 ton/cm².

Example 20

[0058] This example is carried out under the same conditions as those ofExample 18 except that the molding pressure is 40 ton/cm².

COMPARATIVE PREPARATIONS OF NANO-CRYSTAL ALLOY CORES Comparative Example21

[0059] This comparative example is carried out under the same conditionsas those of Example 16 except that the heating treatment for the core isperformed at 500° C. The properties of the manufactured amorphous core,i.e. density, generation of cracks, saturated magnetic flux density,effective permeability in various frequency bands, and permeabilityratio (μ_(1 MHz)/μ_(0 1 MHz)) are shown in Table 3.

Comparative Example 22

[0060] This comparative example is carried out under the same conditionsas those of Example 17 except that the heating treatment for the core isperformed at 450° C. The properties of the manufactured amorphous core,i.e. density, generation of cracks, saturated magnetic flux density,effective permeability in various frequency bands, and permeabilityratio (μ_(1 MHz)/μ_(0 1 MHz)) are shown in Table 3.

Comparative Example 23

[0061] This comparative example is carried out under the same conditionsas those of Example 16 except that the heating treatment for the core isperformed at 65° C. The properties of the manufactured amorphous core,i.e. density, generation of cracks, saturated magnetic flux density,effective permeability in various frequency bands, and permeabilityratio (μ_(1 MHz)/μ_(0 1 MHz)) are shown in Table 3. TABLE 3 Tempera-Saturated Crystalliz- ture for Average Magnetic Example/ ation heatingcrystal Density Flux Permeability Comparative Starting treatmentdiameter of Core Density Effective Permeability (μ_(eff)) Ratio Examplepoint (° C.) (° C.) (nm) (g/cm²) (B_(B)) 0.1 MHz 0.5 MHz 1 MHzμ_(1 MHz)/μ_(0 1 MHz) 16 520 560 15 5.83 1.10 T 67.0 66.8 65.0 0.97 17470 500 17 5.85 1.35 T 63.3 63.0 62.0 0.98 18 470 500 17 5.79 1.31 T62.1 62.0 60.9 0.98 19 520 500 17 6.25 1.39 T 146.7 144.5 135.0 0.92 20470 500 17 6.20 1.38 T 134.4 132.2 125.0 0.93 21 520 500 — 5.75 0.90 T45.2 45.0 44.7 0.99 22 470 450 — 5.76 1.10 T 42.6 42.3 42.1 0.99 23 470650 45 5.86 1.40 T 49.5 49.0 46.2 0.93

[0062] Referring to Table 3, the saturated magnetic flux density is over1.10T in all the preferred embodiments, and the properties of thenano-crystal alloy cores are enhanced by more than 20% compared to theamorphous alloy powder cores of the same composition (Examples 21-23)that were thermally treated below the crystallization temperature. Theeffective permeability in 1 MHz is over 60.0, and its permeability isenhanced by more than 20% compared to the amorphous soft-magnetic alloypowder core composition thermally treated at below the crystallizationtemperature.

[0063] There is little permeability change in the frequency band from0.1 MHz to 1 MHz. The permeability ratio of this nano-crystal alloy coreis over 0.90 in the frequency band of 1 MHz and 0.1 MHz, and shows thelow dependence of the inventive core on frequencies, which means thatthis amorphous core can be used to 1 MHz. When comparing it with a metalcrystal core, the inventive core is similar to or superior to the metalcrystal core in magnetic properties (saturated magnetic flux density andpermeability), and its effective permeability ratio is over 0.90 in thefrequency band to 1 MHz. Therefore, the inventive core can be used intens of megahertz whereas the metal crystal core's appropriate frequencyband is 200 kHz.

[0064] As the core (Comparative Example 23) thermally treated at thetemperature higher than the crystallization starting temperature by 180°has a coarse average crystal diameter, its saturated magnetic fluxdensity is almost the same as the inventive nano-crystal alloy core andits permeability is significantly degraded.

[0065] The inventive amorphous alloy powder core/nano-crystal alloypowder core exhibits excellent high frequency properties has a highmolding density without surface cracking, and shows the satisfactoryinsulation of particles and low dependence on frequencies. In addition,the inventive amorphous alloy powder core/nano-crystal alloy powder corehas a constant permeability in the high frequency band range, and can beused in magnetic materials for electric and electronic devices in thefrequency band from several kilohertz to tens of megahertz.

[0066] While this invention has been described in connection with whatis presently considered to be the most practical and preferredembodiments, it is to be understood that the invention is not limited tothe disclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

What is claimed is:
 1. A method of manufacturing an amorphous alloy corecomprising the steps of: mixing an amorphous alloy powder with asolution made by dissolving a polyimide/phenolic resin binder in anorganic solvent, evenly coating the binder in liquid phase on thesurface of the alloy powder to make a powder of composite particles;molding the power of composite particles; and performing a heatingtreatment thereon.
 2. A method according to claim 1, wherein theamorphous alloy powder is selected from the group consisting of Fe—Si—Bbased alloys, Fe—Al—B based alloys, and Co—Fe—Si—B based alloys.
 3. Amethod according to claim 1, wherein the amount of the binder is 0.5 to3.0 wt % of the total mass.
 4. A method according to claim 1, whereinthe molding is performed at from about room temperature to about 200° C.under a pressure of 10 to 50 ton/cm².
 5. A method according to claim 1,wherein the heating treatment is performed at 150 to 500° C.
 6. A methodaccording to claim 1, further comprising the step of performing aheating treatment on the amorphous alloy powder at less than 500° C.before mixing the amorphous alloy powder in the solution made bydissolving the polyimide resin or phenolic resin in the organic solvent.7. An amorphous alloy core having a saturated magnetic flux density ofmore than 0.80T and a permeability of more than 0.90, measured in 1 MHzand 0.1 MHz.
 8. An amorphous alloy core according to claim 7, whereinthe amorphous alloy core is made by evenly coating a polyimide-based orphenol-based binder on an amorphous alloy powder, and performing acompression molding at less than 200° C.
 9. A method of manufacturing anano-crystal alloy core comprising the steps of: mixing an amorphousalloy powder with a solution made by dissolving a polyimide/phenolicresin binder in an organic solvent, evenly coating the binder in liquidphase on the surface of the alloy powder to make a powder of compositeparticles; molding the power of composite particles at room temperature;and performing a heating treatment thereon at over a crystallizationstarting temperature.
 10. A method according to claim 9, wherein theamorphous alloy powder is selected from the group consisting of Fe—Si—Bbased alloys and Fe—Al—B based alloys.
 11. A method according to claim9, wherein the heating treatment is performed at less than 100° C.higher than the crystallization starting temperature of said amorphousalloy.
 12. A method of manufacturing a nano-crystal alloy corecomprising: performing a heating treatment on an amorphous alloy powderat over a crystallization starting temperature to make a nano-crystalphase, mixing a solution made by dissolving a polyimide/phenolic resinbinder in an organic solvent therewith, evenly coating the binder inliquid phase on the surface of the alloy powder to make a powder ofcomposite particles; and molding the power of composite particles at 100to 300° C.
 13. A method according to claim 12, wherein the amorphousalloy powder is selected from the group consisting of Fe—Si—B basedalloys and Fe—Al—B based alloys.
 14. A method according to claim 12,wherein the heating treatment is performed at less than 100° C. higherthan the crystallization starting temperature of said amorphous alloy.15. A nano-crystal alloy core having a saturated magnetic flux densityof more than 1.10T and a permeability of more than 0.90, measured in 1MHz and 0.1 MHz.
 16. A method of manufacturing an amorphous alloy coreor nano-crystal alloy core by mixing an alloy powder with a solutionmade by dissolving a resin selected from the group consisting of apolyimide resin and a phenolic resin in an organic solvent.